You haven't answered my question in terms of specifics. Judging by this comp, there's not that much difference and current Messi wouldn't look out of place in 18/19 Barca.
Also, keep in mind that Messi was injured mostly during this tournament. This is him vs Porto
Judging from the comp there is a huge difference, which only if you are in denial you can't see.
Stylistically he looks the same, but he can't do the same things.
Here is one specific:
Watch the first 4 min or so of the comp, where he glides his way past tons of defenders centrally in congested and super tight spaces.
That was a trademark thing. He can't do that nowadays.
The clip from tonight's game you posted shows this very clearly a couple of times: see for instance at 0.53 where he can't get past his man and he resorts to turning around just to keep the ball without progressing.
Most of the times nowadays he seems to be kicking the ball first time just because he knows he can't make the run himself.
It's funny that, judging from the clip, Mascherano set up his team really well to find Messi on the counter with acres of open space and runners around him, yet they were unable to make use of it. Messi 18/19 would have scored at least 3 by himself just by receiving in these positions and situations. It's actually part of what he was doing that season, and was set up by EV
PS: I can talk many other aspects he has declined. The only thing that looks to have remained the same is his vertical through-ball